Colloquially it's called a pigskin, but the modern American football is in fact made of cow. Which you'll see in the video below, shot at the Wilson Sporting Goods factory in Ohio.
As Kottke has pointed out, it is fascinating that just a handful--less than ten people--have produced every NFL footbal in the past few decades. I also found it interesting that seven of them are women, and wonder if the players of this all-male game realize that.
Out of all of 'em, I think Glen's got the toughest job--check out the color of his hands.